I. Technological Field
The present invention relates to a method for cleaning a disk-shape glass substrate to be used for e.g. a magnetic disk, and a magnetic disk.
II. Description of Related Art
A magnetic disk having e.g. a magnetic layer formed on a disk-shape glass substrate (hereinafter sometimes referred to simply as a glass substrate) has been widely used for a small hard disk such as a personal digital assistant.
A glass substrate to be used for a magnetic disk is produced usually by cleaning and drying a precisely polished glass substrate.
Cleaning of a glass substrate is carried out commonly by immersing it in a plurality of cleaning fluid tanks such as a cleaner tank and a pure water tank in order and conducting ultrasonic cleaning in each tank. In recent years, for the purpose of securely and effectively removing an abrasive which is firmly attached to the glass substrate, it has been proposed to carry out scrubbing cleaning before or during the ultrasonic cleaning (see JP-A-2002-74653). The scrubbing cleaning is to clean a glass substrate by rotating two scrubbing rollers each having a scrubbing pad formed on its surface in opposite directions so that the glass substrate is sandwiched therebetween, and rotating the glass substrate.
As described above, a glass substrate is becoming used widely for a small hard disk, and the area of a recording area on the main surface is reduced along with the downsizing of the hard disk. Accordingly, in addition to a demand for a high recording density, improvement in the proportion (recording area proportion) of the area which effectively functions as a recording area to the area of the main surface is increasing.
In order to meet the above demands, not only the cleanness on the main surface of the glass substrate has to be improved to achieve a high recording density but also the cleanness on the outer peripheral edge surface of the glass substrate has to be improved, since if the cleanness on the outer peripheral edge surface of the glass substrate is insufficient, the stain present on the edge surface on which the cleanness is insufficient will expand to the main surface of the glass substrate in the process of handling the glass substrate, thus decreasing the recording area proportion.